Figure 5.

Georadar data acquisition map.


#### Table 1.

Conversion from radar into seismic scale.

Identification of Active Faults in Landslide-Prone Regions Using Ground-Penetrating Radar… DOI: http://dx.doi.org/10.5772/intechopen.85397


Table 2.

southern part of Lembang and crossing Cisarua from east to west of Manglayang mountain. Throw of this fault is varying up to 450 m in Pulasari near to the target area. The Lembang fault was created during the Pleistosen era (about 500,000 years

volcano eruption activities are distributed into southern part of Bandung.

antenna. Most of the profile was selected perpendicular to the fault.

this area. Sketch of data gathering in this area is shown in Figure 5. The data collection was conducted using common-offset method with 25 and 50 MHz

In the end of Miocene, series of mountains and folds are created in the northern part and in the southern part which become series of volcanos. In the breaking time of Pliocene era, there is no activity of volcanoes and sedimentation, and in the end of Pliocene era, series of mountains were created, and sediments in the northern part were folded and shifted into northern part of Bandung. Materials as a result of

To detect the existence of Lembang fault, a georadar survey was conducted in

All the data are processed using Seismic Unix (SU) software by performing the scaling on the time sampling rate from nanosecond to millisecond (ms), frequency from megahertz to hertz and velocity from m/ns to m/μs. The details of conversion

The processing data includes filtering using band-pass filter (10, 20, 30, 50) MHz for antenna 25 MHz and (10, 30, 70, 100) MHz for 50 Hz, AGC, and velocity analysis based on hyperbole fitting curve. The velocity obtained from hyperbole fitting curve is shown in Table 2. This velocity model was used to convert time

Parameters True value Scaled value Time sampling rate 1.4 ns 1.4 ms Nyquist frequency 357 MHz 357 Hz Offset 1 m 1 m Radar speed in air 0.3 m/ns 300 m/μ

ago) [6].

Earth Crust

Figure 5.

Table 1.

54

Georadar data acquisition map.

Conversion from radar into seismic scale.

factor are shown in Table 1.

Velocity model extracted from hyperbole fitting curve during velocity analysis.

domain into depth domain in the profile. In general, the velocity is quite high because the lithology is dominated by tuff, andesite, and breccia volcanic.

## 4. Result and discussion

Out of several profiles which were studied, profile 03 displayed the large fault in the radargram which is associated with a main Lembang fault. In the other profiles, there are some small fault systems. Based on the velocity analysis, the structure of Lembang fault is a conductive area where the velocity decreases with depth. Profile in Figure 6 which is taken perpendicular to the fault shows a normal fault system. The foot wall is located in the northern part and hanging wall in the southern part. The position of foot wall part is lower about 7–8 m compared to the hanging wall part. The structure of this area consists of basement which is indicated by a free reflection area and sediment bedding in the horizontal layer. Above the foot wall part, there is a pattern of unconformity.

In Figure 6, the top of basement formation is interpreted as the blue line indicates a normal fault. The folded reflection can be resulted as post fault due to the compression from the northern part; the horizontal bedding is folded as small anticline. Cracking in the shoulder of road around this profile indicates that the fault reaches the surface. Those crack lies in the west–east direction where the northern part is lower than southern part. Previous study mentioned that this active

Figure 6. Cross section taken perpendicular to the fault.

fault has a movement rate per year about 0.3–1.4 cm/year [6]. Instability of this area due to the activities of this fault especially the possible earthquake needs to be monitored further to avoid the further effect like landslide which can damage the urban and suburban area around this fault.

Small faults around the main fault also recorded in other profiles.

is appearing in this area.

DOI: http://dx.doi.org/10.5772/intechopen.85397

the soil mechanism in this area.

5. Conclusion

consciously.

Author details

Maman Hermana<sup>1</sup>

57

\*, Maya Genisa<sup>2</sup>

2 YARSI University, Jakarta, Indonesia

provided the original work is properly cited.

1 University Technology of PETRONAS, Perak, Malaysia

\*Address all correspondence to: maman.hermana@utp.edu.my

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Figures 7 and 8 show the pattern of small fault systems which are still related to the activity of the main fault. Profiles 9 and 10 as shown in Figures 4 and 5 are taken perpendicular also to the main fault direction. The main fault is not recorded in these profiles. However, the diffraction pattern which indicates small fault system

Identification of Active Faults in Landslide-Prone Regions Using Ground-Penetrating Radar…

The subduction and compression process in the north–south direction also produces other local fault system. Because the length of this fault is only 29 km, the maximum earthquake due to the energy release in this area is predicted that the earthquake magnitude will not be more than 6 in Richter scale. Tectonic activity record in this area showed that the focus of earthquake is located in the depth of 3– 7 km. The earthquake activities are also related to the continuity of three main fault in Bandung area which are Cimandiri fault, Lembang fault, and Baribis fault [6]. Even though the earthquake recorded in this area are not strong earthquakes, because this area is one of the tourism object locations in Bandung and high population around this area, the monitoring of possible hazard needs to be continued. A small earthquake is possible to activate that fault which can trigger instability of

Lembang fault which is located near the urban area with high population density is successfully imaged using georadar method. Based on radargram result, the foot wall part of Lembang fault is located in the northern part, and hanging wall is located in the southern part. The subsurface structure in this area is dominated by basement and sediment layers. Due to the location of this fault which is near the urban area with high population, further investigation to mitigate the potential of landslide, instability, and activity of this fault needs to be monitored. A CMP survey type can be proposed to be used to improve velocity information; hence, the depth of structure in the subsurface can be improved. A monitoring on the movement of this fault activity using GPS needs to be performed to monitor these activities

, Luluan A. Lubis<sup>1</sup> and Chow Weng Sum<sup>1</sup>

Figure 7. Profile 9 taken perpendicular to the fault line.

Figure 8. Profile 10 taken perpendicular to the fault direction.

Identification of Active Faults in Landslide-Prone Regions Using Ground-Penetrating Radar… DOI: http://dx.doi.org/10.5772/intechopen.85397

Small faults around the main fault also recorded in other profiles. Figures 7 and 8 show the pattern of small fault systems which are still related to the activity of the main fault. Profiles 9 and 10 as shown in Figures 4 and 5 are taken perpendicular also to the main fault direction. The main fault is not recorded in these profiles. However, the diffraction pattern which indicates small fault system is appearing in this area.

The subduction and compression process in the north–south direction also produces other local fault system. Because the length of this fault is only 29 km, the maximum earthquake due to the energy release in this area is predicted that the earthquake magnitude will not be more than 6 in Richter scale. Tectonic activity record in this area showed that the focus of earthquake is located in the depth of 3– 7 km. The earthquake activities are also related to the continuity of three main fault in Bandung area which are Cimandiri fault, Lembang fault, and Baribis fault [6]. Even though the earthquake recorded in this area are not strong earthquakes, because this area is one of the tourism object locations in Bandung and high population around this area, the monitoring of possible hazard needs to be continued. A small earthquake is possible to activate that fault which can trigger instability of the soil mechanism in this area.

## 5. Conclusion

fault has a movement rate per year about 0.3–1.4 cm/year [6]. Instability of this area due to the activities of this fault especially the possible earthquake needs to be monitored further to avoid the further effect like landslide which can damage the

urban and suburban area around this fault.

Figure 7.

Earth Crust

Figure 8.

56

Profile 9 taken perpendicular to the fault line.

Profile 10 taken perpendicular to the fault direction.

Lembang fault which is located near the urban area with high population density is successfully imaged using georadar method. Based on radargram result, the foot wall part of Lembang fault is located in the northern part, and hanging wall is located in the southern part. The subsurface structure in this area is dominated by basement and sediment layers. Due to the location of this fault which is near the urban area with high population, further investigation to mitigate the potential of landslide, instability, and activity of this fault needs to be monitored. A CMP survey type can be proposed to be used to improve velocity information; hence, the depth of structure in the subsurface can be improved. A monitoring on the movement of this fault activity using GPS needs to be performed to monitor these activities consciously.
